Moccasin Dam, near the town of Groveland, on a small reservoir, was at risk of failure amid heavy rain.

The National Weather Service on Thursday (March 22) issued a flash flood warning for part of the Sierra foothills near Yosemite National Park, saying that Moccasin Dam in Tuolumne County, Calif., was at risk of “imminent failure.”

The dam was later determined to be sound and in no danger of failing, according to The Mercury News.

The 60-foot high dam, built of compacted rock on a small reservoir near the town of Groveland west of Yosemite National Park, is part of the Hetch Hetchy water system that serves the Bay Area. If the dam fails, the water will flow into Don Pedro Reservoir one mile downstream, the Tuolumne County Sheriff’s office said. That reservoir, which is nearly 4,000 times the size of Moccasin Reservoir, was 84% full Thursday, with enough room to hold the extra water.

“There is no threat to the Bay Area’s water supply at this time, and all people potentially in harm’s way have been evacuated out of an abundance of caution,” the San Francisco Public Utilities Commission said in a statement on Thursday. “The dam has not overtopped and is still intact.”

The Tuolumne County Sheriff’s office said on its Facebook page: “Facilities downstream of the dam along the creek have all been evacuated. Precautionary evacuations are being conducted at Moccasin Point Campground. The town of Moccasin is above the dam and will not be impacted.”

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